RALEIGH Tiny Asian beetles that tunnel into dead wood are invading the U.S. But in North Carolina, they're boring holes into living trees as well as dead ones.

Beetles like these may have the potential to devastate trees worldwide, N.C. State researchers said in a report released last week.

Two destructive species of ambrosia beetles from Asia have already arrived in North Carolina. The redbay ambrosia beetle was found in the state for the first time in Bladen County just this April, while granulate ambrosia beetles have been around for decades.

In North Carolina, redbay ambrosia beetles kill ecologically important trees such as sassafras, redbay and the endangered pondberry.

But the beetles are a threat to the economy as well as to ecology.

Redbay ambrosia beetles have ravaged avocado orchards in Florida, while granulate ambrosia beetles attack peach, plum and pecan trees, along with dogwoods, Japanese maples and crepe myrtles.

"It's one of the most important pests of nurseries," said Dr. Steve Frank, an entomologist at N.C. State University who was not affiliated with the report.

Redbay and granulate ambrosia beetles are two of dozens of foreign ambrosia beetle species living in North Carolina. But the others are all harmless, as are hundreds more native ambrosia beetle species who make their homes in dead or dying trees.

Why do only some ambrosia beetles attack living trees? That's a question researchers are still trying to answer, said Dr. Jiri Hulcr, an N.C. State researcher and lead author of the report, which came out Wednesday.

Fungus and confusion

Ambrosia beetles are very different from better known pine beetles. Pine beetles kill a tree by destroying vital parts of the trunk as they eat, but ambrosia beetles don't actually eat wood at all.

Instead, they bore into trees and plant fungus in the tunnels. The fungus extracts nutrients from the tree, and then the beetles feed on the fungus. In effect, ambrosia beetles are farmers.

There are more than 3,500 ambrosia beetle species living all over the world. In their native forests, they plant their fungus only in dead or dying trees. The beetles are attracted to certain chemicals in the smell of dying and rotting wood, such as ethanol, the same chemical found in alcoholic drinks.

"If you open up a beer in the forest, the beetles are actually attracted to you," Hulcr said. "It's a very easy way to catch ambrosia beetles."

When the beetles end up in a new environment - if they are transported across the ocean in a shipping crate, for instance - they can get confused. Some living trees in their new home smell like dead wood to the beetles, and they start boring into trees to plant their fungus while the trees are still alive.

For many trees, Hulcr said, this isn't too much of a problem. In a few cases, though, a tree overreacts to the fungus planted by the beetle. Much like in a severe allergic reaction, the tree works so hard to kill the fungus that it winds up killing itself instead.

Only certain tree species have this "allergic" response to the beetles' fungus, and the beetles mistake only certain tree species for dead wood. Both have to happen for beetles to cause harm. Luckily, this only happens for a few kinds of trees.

And of course, only some kinds of beetles get confused and make mistakes in the first place.

Ineffective treatment

Without a good understanding of what goes wrong when beetles arrive in a foreign environment, researchers can't predict which of the thousands of ambrosia beetle species worldwide may one day pose a threat to economically and ecologically important trees.

In addition, the only tools to destroy the beetles and the fungus they plant are unreliable at best.

Because ambrosia beetles bore inside trees, spraying pesticides on the outside doesn't kill them. Injecting susceptible trees with fungicide before beetles invade can sometimes prevent infestations, but it's expensive, inefficient and not always effective.

"Right now, we have absolutely no weapons against these beetles," Hulcr said.

Without effective ways to kill ambrosia beetles, the best strategy for fighting them is prevention.

Beetles can move up to 20 miles a year on their own, but they often hitch a ride in firewood, wood chips, or downed trees that people send to landfills, according to Robert Trickel, head of the forest health branch in the N.C. Division of Forest Resources.

"We're asking people to not move firewood," Trickel said. This and other simple steps such as disposing of dead trees on the property where they fell, he said, can help to slow the beetles' spread.